The use of Canon EOS cameras and compatible lenses for recording HD movies is becoming increasingly popular, providing the opportunity for Canon to optimize the way in which their cameras and lenses function, not just for capturing still images, but also for shooting movies.

With the release of the EF-S 18-135mm f/3.5-5.6 IS STM and the EF 40mm f/2.8 STM, Canon is further enhancing the performance of digital SLR cameras for shooting
HD video.

When shooting still images, an ideal lens AF system:

Zips into sharp focus as quickly as possible

Is able to focus-track a rapidly-moving subject when shooting through
the viewfinder

When shooting movies, an ideal lens AF system:

Has a smooth, relatively slow focus transition

Can focus in very smooth “steps”, allowing the image sensor to
detect sharpness

Performs very quietly, reducing operation noise in the recording

To meet the ideal AF system demands for today’s HD digital SLRs, Canon has designed two lenses using a new stepping motor (STM)

The STM provides AF that is optimized for video and Live View focus tasks —
but still quick and practical for everyday still image shooting.

This new AF stepping motor serves as the core of two new Canon lenses: